Electrical conductor terminal assembly

ABSTRACT

An assembly for making an electrical connection between a flat terminal strap and an aluminum conductor, comprising a U-shaped saddle member including a pair of leg sections adapted to straddle the strap, a bolt captured in a free-turning relation in the bridging section between the leg sections and threadedly engaging the strap, a resilient washer positioned between the bottom of the head of the bolt and the bridging section of the saddle member, and wherein the saddle member is aluminum and the leg sections of the saddle member are straight, parallel and of arcuate cross section.

Klein et al.

[11] 3,824,555 [451 July 16, 1974 ELECTRICAL CONDUCTOR TERMINAL ASSEMBLYInventors: Keith William Klein, Simsbury;

Joseph Michael Palmieri, Southington, both of Conn.

General Electric Company, New York, NY.

Filedz Apr. 2, 1973 Appl. No.: 347,127

Assignee:

U.S. Cl. 339/246, 339/269 Int. Cl HOlr 7/24 Field of Search 339/244,246, 269, 271;

24/125 R, 135 B, 81 CC References Cited FOREIGN PATENTS OR APPLICATIONS632,048 11/1949 Great Britain 339/246 Primary ExaminerJoseph H. McGlynnAttorney, Agent, or FirmRobert A. Cahill; Philip L. Schlamp; Frank L.Neuhauser [57] ABSTRACT An assembly for making an electrical connectionbetween a flat terminal strap and an aluminum conductor, comprising aU-shaped saddle member including a pair of leg sections adapted tostraddle the strap, a bolt captured in a free-turning relation in thebridging section between the leg sections and threadedly engaging thestrap, a resilient washer positioned between the bottom of the head ofthe bolt and the bridging section of the saddle member, and wherein thesaddle member is aluminum andthe leg sections of the saddle member arestraight, parallel and of arcuate cross sectron.

2 Claims, 6 Drawing Figures ELECTRICAL CONDUCTOR TERMINAL ASSEMBLYBACKGROUND OF THE INVENTION Heretofore difficulties have been generallyexperienced in making tight electrically dependable connections betweenwires and the flat terminal straps commonly used in various electricaldevices such, for example, as molded case circuit breakers, switches,relays and the like. More specifically, in such devices electricalconnections are generally made between the terminal straps and the wiresby clamping devices of various kinds serving to hold the wires andterminal straps in a tight electrical contact. One example of suchconnectors is shown in U.S. Pat. No. 3,191,140Coldren. However, thesedevices place the wire and cooperating strap and clamping elements incompression, and when the wire and any of such cooperating elements areformed of aluminum or other relatively soft materials there is atendency for them to cold flow or deform under the compressive stressestherein. This deformation, in turn, adversely affects the mechanical andelectrical connections between the elements. A connector described aseffective for overcoming this problem in the connection of two aluminumwires is shown in U.S. Pat. No. 2,77l,59lVordtriede.

ln connectors of the presently considered type the wire tends to assumea flattened cross-sectional configuration between the flat terminalstrap and the flat inner surface of the saddle member and thus becomeloosened mechanically and less intimately connected electrically.Similarly, the terminal strap is often formed of aluminum orsurface-coated with aluminum or other relatively soft metal for desiredheat transfer and dissipation purposes and to provide for improvedelectrical contact with the aluminum wire. In this case the compressiveeffect of the wire on the surface of the strap can cause the underlyingaluminum or other soft metal of the strap surface to flow outwardly fromunder the wire and thus also cause loosening of the wire and undesiredeffects in the electrical contact therebetween. Due to the desirableheat transfer and dissipation properties of aluminum, the clampingelements are advantageously wholly formed of aluminum. However, here toothe compressive stresses induced in the clamp legs can cause a tendencyfor them to bow and thus relieve somewhat the contacting pressurebetween the wire and terminal strap.

In addition to the above-reference advantages of forming the clampingelements of aluminum, the provision of a connection assembly wherein theterminal strap, wire conductor and clamping element are all formed ofaluminum is desirable because of resultant cost and weight advantages aswell as protection against corrosion due to galvanic action which isgenerally encountered when parts formed of dissimilar metals are used.Thus, it is highly desirable to provide an essentially all-aluminumassembly which is also effective and dependable in maintainingsatisfactory electrical contact of parts regardless of possibledeformation in the aluminum pars when maintained under compressivestresses.

Furthermore, in devices embodying electrical connector assemblies of theabove-discussed type space is often at a premium. For example. incertain molded case circuit breakers the lateral dimensions of theterminal straps must, owing to available space considerations, beminimized as must be the corresponding dimensions of cooperating wireclamping elements. Yet it is desirable that the space in the assemblyfor receiving the wire to be connected be maximized to enable greaterchoice inthe gauge of wire to be employed.

Still further, it is desirable that the parts of electrical connectorassemblies be adapted for cooperating in a manner which facilitates themaking of a dependable initial electrical contact between the parts andfor minimizing any undesired relative motion between such parts whichcould adversely affect such contact during normal operating lift of anassembly.

OBJECT OF THE INVENTION A general object of the present invention is toprovide an electrical connector adapted for assuring reliable electricalconnections between flat terminal straps of electrical devices and wireconductors formed of aluminum and other relatively soft metals whichhave a tendency to deform under compressive stresses induced byelectrical clamping elements and thereby adversely affect the electricalintegrity of the connections. I l

Another object of the present invention is to provide a dependableelectrical connector which is particularly suited for use whereconnection space is at a premium but which isalso effective formaximizing the gauge of wire conductor usable therein.

Still another object of the present invention is to provide anelectrical connector which, in cooperation with aluminum terminal strapsand aluminum wire conductors, affords an essentially wholly aluminumassembly in order to gain desired cost, weight, electrical and thermalconductivity and corrosion resistance advantages while also affordingthe electrical contact dependability desired.

SUMMARY OF THE INVENTION In accordance with one embodiment of theinvention, an assembly is provided for making connection to a flatterminal strap which can comprise part of an electrical'device such as amolded case circuit breaker, a relay, a switch or'any other similarstructure. The strap is provided near its end with a tapped aperture toreceive a bolt or screw adapted for drawing a conductive clampingelement down onto the strap in a manner effective for securing a wireconductor in electrical contact with the strap.

The strap is rectangular in cross section to provide a flat uppersurface to cooperate with the wire, and parallel vertical sides tocooperate effectively with the clamping element. More specifically, theclamping element is a conductive saddle member formed with a pair ofpendent leg sections and a bridging section joining the leg sections.The bridging section is centrally apertured and has a flat extensivebearing surface surrounding the aperture therein. Suitably staked in thebridging aperture so as to be retained therein in relatively loosefree-turning relation is a drawbolt or screw which has a threaded shankextending downward between the leg sections of the saddle member forbeing threaded into the tapped aperture of the terminal strap. When awire conductor is disposed between the saddle member and strap and thedrawbolt is tightened, the wire is compressed between the flat lowerside of the bridging section of the saddle member and the flat uppersurface of the strap for effecting a desired electrical contact betweenthe wire and strap.

The leg sections are arcuate in cross section to provide maximum radialspace between thebolt shank and the. leg sections and to rigidize thelegs in parallel spaced relationAlso, the opposed edges of the legsections are parallel and predeterminedlyspaced apart to provide aclose-fitting sliding relation with respect to the terminal strappositioned therebetween.

The drawbolt head extends broadly over the bearing surface on thebridging section of the saddle member and includes a flat bearingsurfaceon its underside facing the bearing surface on the bridging section.Loosely mounted on the bolt and positioned between the bearing surfaceson the bolt and bridging section is a concavo-convex spring washer. Theconvex surface of the spring washer engages the flat bearing surfaceunder the bolt head and the rim extends broadly outwardly and engagesand bearing surface'on the bridging section of the saddle member.

DESCRIPTION OF THE DRAWING In the drawing, I FIG. 1 is a perspectiveview of an electrical connection assembly embodying a preferred form ofthe invention;

FIG. 2 is an elevational view of the assembly of FIG. I with theterminal strap and wire conductor illustrated in'cross section;

FIG. 3 is a bottom plan view of the assembly shown in FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view il- DETAILEDDESCRIPTION OF APREFERRED EMBODIMENT The inventin is shown in FIG. 1-3effecting an electrical connection between a flat terminal strap 10 anda wire conductor 11. The strap 10 is elongated, rectangular in crosssection, and typical of the terminal straps or lugs which are used asexternal terminals in many electrical devices such as molded casecircuit breakers, relays, switches and the like. The wire conductor 11may be a single conductor, as shown, or a multi-strand conductor and, aswill be brought out in detail hereinafter, the present invention is mostadvantageously employed when the wire is formed of aluminum or otherrelatively soft metals including copper.-

Cooperating with the strap 10 to secure the wire 11 in firm electricalcontact therewith is a connector 12 comprising a generally U-shapedfloating clamp or saddle member 13. The saddle member 13 is formed toinclude a pair of pendent leg sections 14 and a bridging section 15joining the leg sections. The leg sections 14 constitute opposed spacedsections of a cylindrical section depending from the bridging sectionand, as best seen in F lG..3, are arcuate in cross section throughoutthe lengths thereof. Additionally, the opposed inner edges 16 of the legsections are predeterminedly spaced for receiving the terminal strap 10therebetween in closely fitting sliding and guiding relation, thepurpose for which will be brought out in detail hereinafter.

The bridging section 15 is providedwith a centrally located aperture 17in which, as best seen in FIGS. 3 and 4, there is mounted adrawbolt orscrew 18. The bolt 18 includes a head 19, which is preferably slotted,as shown, for screw driver tightening but which can, if desired, beprovided with lands for wrench tightening, a threaded shank portion 20and an intermediate reduced section 21. The reduced section 21 islocated in the bridging section aperture 17 and is smaller in diameterthan the aperture. Also, the region of the bridging section constitutingthe underside edgeof the aperture 17 is staked or inwardly displaced toa diameter less than the diameter of the threaded portion of the shank.This arrangement is effective for retaining the bolt 18 in a relativelyloose, free-turning relation in the bridging section.

The threaded shank 20 of the bolt 18 is adapted for threadedly engagingthe terminal strap 10 in the manner illustrated and, when tightened, iseffective for drawing the terminal strap 10 toward the bridging sectionof the saddle member and into a secure contacting relation with the wireconductor 11 positioned therebetween. r

The relative dimensioning of the strap 10 and the spacing to provide aclose fit and the straight, parallel vertical edges 16 on the legsections of the saddle member all cooperate effectively to provide forvertical guided movement of the strap into, engagement with the wire andto minimize any other relative movement of the parts during thetightening of the bolt or during subsequent operating life, which lattermovement, if permitted, could result in adversely affecting the wireholding effect of the arrangement and the electrical contact between thewire and strap.

Additionally, there is provided between the head 19 of the bolt and thebridging section 15 of the saddle member a concavo-convex or dishedspring washer 22. More specifically, the upper surface and the bolt headis enlarged and of a diameter greater than the width of the bridgingsection. Also,' the underside of the bolt head is flat and thistogether'with the large diameter of the head effectively adapts it forpresenting a bearing surface opposing and extending substantially overthe bearing surface surrounding the aperture in the bridging section.Disposed between these opposed bearing surfaces and mounted loosely onthe reduced section of the bolt shank is the above-referenced springwasher 22 which preferably also has an outer diameter greater than thewidth of the bridging section and the outer diameter of the bolt head.The spring washer 22 is preferably of the so-called Belleville type"-and its purpose and the manner in which it effectively cooperates withthe other elements in the described assembly will now be described indetail.

The disclosed arrangement, as indicatedabove, is most advantageouslyemployed where the wire conductor 10 is formed of aluminum or anotherrelatively soft metal and where such conductors have a tendency to coldflow or deform under pressure. More specifically, when aluminum andother soft metal conductors are clamped or held in compression in aclamping'conne'ctor of the described type, the wire section held firmlyunder Compressive stress between the terminal strap and saddle membertends to cold flow outwardly or flatten in cross section. Unlessappropriate compensating means is provided, this flattening of the wirecan cause it to become loosened in the clamp or to degrade theelectrical contact between the wire and terminal, Similarly, it is oftendesirable to have the terminal strap either wholly formed of aluminumand coated with tin, or formed of another metal and surface coated withtin or aluminum, and to form the saddle member of aluminum also, all forthe purpose of enhanced thermal and electrical conductivity as well asweight and cost advantages and avoidance of corrosion due to galvanicaction. Using aluminum for the saddle member, strap and wire alsoaffords greater uniformity of the coefficients of expansion of thecooperating elements and thus minimizes chances of undesirable looseningdue to differences in thermal expansion and contraction of parts duringoperating life.

However, when a terminal strap or the saddle member are formed of,or-coated with a soft metal, they too are subject to a certain amount ofcold flow or deformation under compressive stresses induced by thetightening of the drawbolt. This can occur at the surfaces thereofengaged by the wire and can contribute to the looseningof the wire orcan adversely affect the electrical contact between the wire andterminal. The just-described adverse effects are avoided or greatlyminimized by the arrangement including the large bolt head, theextensive bearing surfaces on the bolt head and bridging section and thelarge diameter Belleville washer therebetween. More specifically, thelarge bolt head and large underside bearing surface enable substantialarea contact with the spring washer and resultant substantial pressureto be brought to bear and to be maintained on an extensive area of theupper surface of the spring washer. This pressure is substantiallygreater than that which can be afforded, for example, by the circularline of contact arrangement shown in U.S. Pat. No. 2,771,59l-Vrdtrided,and thus it serves to readily compress the spring washer; and the springwasher, owing to its substantial diameter and the relatively largebearing surface on the bridging section of the saddle member, transmitsand maintains considerable spring pressure on the saddle member forurging it into firm contact with the wire conductor and therebymaintaining the wire conductor in firm contacting relation with thestrap. Thus, the spring follows up or compensates for any deformation ofthe wire or other soft metal elements which could otherwise affect theelectrical contact therebetween.

In the described connector, the large bolt head and the broad extensionof the Belleville spring over the large bearing surface on the bridgingsection of the saddle member together with the loose fit of the saddlemember and spring on the bolt shank, serve to cooperate in uniformlydrawing the strap up into the saddle member and in enabling an assemblerto quickly and securely fasten a wire conductor in place and in contactwith the terminal strap. Also, the abovedescribed predetermined relativedimensioning of the strap and the close fit of the straight parallelinner edges of the leg sections astraddle the strap causes the strap tomove and be guided substantially straight upwardly between the legsections and into clamping engagement with a minimum of any wobbling"movement of the saddle member during assembly. This serves to providemore uniform dependable clamping action of the assembly.

The present invention is also effective for maximizing the diameter ofwire that may be used with a terminal strap of a given width. This isparticularly advantageous where space is at a premium, such as in theapplication illustrated in FIG. 6, wherein the case 23 of the devicewhich may, for example, be a molded case circuit breaker, has arelatively small recess 24 in which the external portion of the terminalstrap 10 is located and the strap must necessarily be limited to aparticular width. As seen in FIG. 3, when the wire diameter is less thanthe dimension from the bolt shank to the side edges of the leg sections,the arcuate cross-sectional configuration of the legs serves only onefunction, namely, to rigidize the leg sections. This better adapts athinner gauge and relatively soft metal, such as aluminium stock, foruse in fabricating the saddle member.

However, the arcuate cross-sectional configuration of the legs serves avery effective second function when it is desired to use a largerdiameter wire. More specifically, and as best seen in FIG. 5, thearcuate cross section of the legs provides spaces between the bolt shankand inner surfaces of the legs which are substantially greater in radiallength than the available spaces would be if the legs had flat innersurfaces of the type shown, for example, in. U.S. Pat. No.3,191,l40-Coldren. Thus, a relatively large diameter conductor 25 can bebent and inserted into the space between the bolt shank and leg section.A portion of the wire may extend slightly over the outer edge of theterminal strap but the wire would be securely clamped between the strapand saddle member and adequate electrical contact would be affordedbetween the wire and substantial engaging surfaces of the terminalstrap.

Various modifications may be made in the connector assembly illustratedwithout departing from the invention, and other modifications will occurto persons familiar with and skilled in the art when exposed to thepresent invention. It is therefore intended, by the appended claims, tocover all such modifications as fully within the true spirit and scopeof the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A terminal connector for making an electrical connection to analuminum wire conductor, said connector comprising:

a. a flat terminal strap of rectangular cross section and having, 1. atleast a contact surface portion of relatively soft metal and, 2. athreaded aperture extending through said contact surface portion; b. analuminum saddle member having,

1. a pair of pendent parallel leg sections for straddling said strap,and 2. a bridging section joining said leg sections and having acentrally located aperture and a flat bearing surface surrounding saidaperture; c. a drawbolt retained in free-turning relation in saidaperture in said saddle member and having, 1. a head with a substantialflat bearing surface on the underside thereof and extending broadly oversaid bridging section of said saddle member, and

2-. a threaded shank extending between the legs of said saddle memberfor threadedly engaging said aperture in said strap and effective whensaid bolt is tightened for drawing said contact surface of said strapinto conductive engagement with said aluminum wire conductor disposedbetween said strap and saddle member; and d. a spring washer mounted onsaid bolt between said bearing surfaces on said saddle member and saidbolt head, said washer extending outwardly of said bolt head and broadlyover said bridge of said saddle member, and effective when compressed bythe tightening of said bolt to provide a continuous compressive force onsaid aluminum conductor to maintain a satisfactory electrical contactwith said strap regardless of any tendency of said conductor orconnector parts to deform under pressure.

2. An assembly for making a reliable electrical connection to analuminum wire comprising:

a. a flat terminal strap of rectangular cross section and having,

l. at least a contact surface portion of relatively soft metal and,

2. a threaded aperture extending through said contact surface portion;

b. an aluminum saddle member having,

1. a pair of legs constituting opposed sections of a cylinder and havingstraight parallel inner edges straddling and in closely fitting slidingrelationship with said strap, and

2. a bridging section joining said legs and having a centrally locatedaperture, a flat bearing surface on the outer surface of said sectionsurrounding said aperture and being extensive relative to the surface ofsaid bridging section;

c. a drawbolt retained in free-turning relation in said aperture in saidsaddle member and having,

1. a head with a flat bearing surface on the underside thereof which isextensive in relation to the surface of said bridging section of saidsaddle member, and

2. a threaded shank extending between the legs of said saddle member andthreaded in said aperture in said strap, and effective when said bolt istightened for drawing said contact surface on said strap into conductiveengagement with an aluminum wire positioned between said strap andsaddle member; and

d. a concavo-convex spring washer mounted on said bolt between saidbearing surfaces of said saddle member and said bolt head and effectivewhen compressed by the tightening of said bolt to provide a continuouscompressive force on said aluminum wire through said strap to compensatefor any deformation of the aluminum under pressure and thereby maintaina satisfactory electrical connection between said wire and said contactsurface of said strap.

1. A terminal connector for making an electrical connection to analuminum wire conductor, said connector comprising: a. a flat terminalstrap of rectangular cross section and having,
 1. at least a contactsurface portion of relatively soft metal and,
 2. a threaded apertureextending through said contact surface portion; b. an aluminum saddlemember having,
 1. a pair of pendent parallel leg sections for straddlingsaid strap, and
 2. a bridging section joining said leg sections andhaving a centrally located aperture and a flat bearing surfacesurrounding said aperture; c. a drawbolt retained in free-turningrelation in said aperture in said saddle member and having,
 1. a headwith a substantial flat bearing surface on the underside thereof andextending broadly over said bridging section of said saddle member, and2. a threaded shank extending between the legs of said saddle member forthreadedly engaging said aperture in said strap and effective when saidbolt is tightened for drawing said contact surface of said strap intoconductive engagement with said aluminum wire conductor disposed betweensaid strap and saddle member; and d. a spring washer mounted on saidbolt between said bearing surfaces on said saddle member and said bolthead, said washer extending outwardly of said bolt head and broadly oversaid bridge of said saddle member, and effective when compressed by thetightening of said bolt to provide a continuous compressive force onsaid aluminum conductor to maintain a satisfactory electrical contactwith said strap regardless of any tendency of said conductor orconnector parts to deform under pressure.
 2. a threaded shank extendingbetween the legs of said saddle member and threaded in said aperture insaid strap, and effective when said bolt is tightened for drawing saidcontact surface on said strap into conductive engagement with analuminum wire positioned between said strap and saddle member; and d. aconcavo-convex spring washer mounted on said bolt between said bearingsurfaces of said saddle member and said bolt head and effective whencompressed by the tightening of said bolt to provide a continuouscompressive force on said aluminum wire through said strap to compensatefor any deformation of the aluminum under pressure and thereby maintaina satisfactory electrical connection between said wire and said contactsurface of said strap.
 2. a bridging section joining said legs andhaving a centrally located aperture, a flat bearing surface on the outersurface of said section surrounding said aperture and being extensiverelative to the surface of said bridging section; c. a drawbolt retainedin free-turning relation in said aperture in said saddle member andhaving,
 2. a threaded aperture extending through said contact surfaceportion; b. an aluminum saddle member having,
 2. An assembly for makinga reliable electrical connection to an aluminum wire comprising: a. aflat terminal strap of rectangular cross section and having,
 2. athreaded shank extending between the legs of said saddle member forthreadedly engaging said aperture in said strap and effective when saidbolt is tightened for drawing said contact surface of said strap intoconductive engagement with said aluminum wire conductor disposed betweensaid strap and saddle member; and d. a spring washer mounted on saidbolt between said bearing surfaces on said saddle member and said bolthead, said washer extending outwardly of said bolt head and broadly oversaid bridge of said saddle member, and effective when compressed by thetightening of said bolt to provide a continuous compressive force onsaid aluminum conductor to maintain a satisfactory electrical contactwith said strap regardless of any tendency of said conductor orconnector parts to deform under pressure.
 2. a bridging section joiningsaid leg sections and having a centrally located aperture and a flatbearing surface surrounding said aperture; c. a drawbolt retained infree-turning relation in said aperture in said saddle member and having,2. a threaded aperture extending through said contact surface portion;b. an aluminum saddle member having,